The lack of no-fault divorce in England and Wales is forcing separating couples into unnecessary and unsuccessful courtroom battles to establish who caused the breakdown, according to a report by the Nuffield Foundation.

The charitable trust’s detailed study of nearly 500 divorces, led by Prof Liz Trinder of Exeter university, finds that many “defended cases are triggered by the law itself” which is out of step with most other jurisdictions in Europe and North America.

The only ground for divorce in England and Wales is irretrievable breakdown of a marriage. There are five specific types, three of which require allegations of fault: adultery, behaviour and desertion. Claimants in contested cases have to prove they have lived apart continuously for five years.

In rare cases where divorces are resisted, the report said, disputes degenerate into who should be blamed and are eventually “settled, rather than decided” by a judge.

“The outcomes ... reflect the relative bargaining capacity of the parties, not an inquiry into the truth of allegations. The court’s willingness to accept the results of some deals appeared intellectually dishonest, even if it did bring an end to a damaging dispute,” the study said.

The report comes ahead of a supreme court hearing next month into the case of Owens v Owens, the only successfully defended divorce case in recent years. Tini Owens, who is in her sixties, claims she has been left trapped in a “loveless and desperately unhappy” marriage after judges refused to allow her to divorce her husband of 40 years.

Trinder said: “The divorce law is now nearly 50 years old and reform is long overdue. Our interviewees told us how difficult marriage breakdown is, yet the law makes the legal divorce even more difficult than it needs to be.

“Having to blame one person to get a divorce does not help and in most cases is unfair. And the court is not able to investigate why a marriage has broken down and recognises anyway that it is a fool’s errand.

“While the supreme court may find a way to grant Mrs Owens her divorce, [it] can only interpret the law. It requires parliament to change it. Reforming the divorce law to remove the requirement for ‘fault’ and replacing it with a notification system would be a clearer and more honest approach, that would also be fairer, more child-centred and cost-effective.”

Defending a divorce is emotionally demanding and few can afford the typical legal fees of around £6,000. Family lawyers generally discourage defence, viewing it as expensive, counter-productive and futile.

Jo Edwards, head of family law at the London firm Forsters and former chair of Resolution, the national family lawyers’ association, said the report “brings into sharp focus what most practitioners have long known – that fault-based divorce is futile, pitting couples against each other in a way which is wholly unnecessary.

“It leaves people wanting the opportunity to put their side of the story as to why a marriage has ended, but finding barriers to doing so. Where a defence is filed, the law undoubtedly causes disputes.”

She added: “It is even harder for the growing number of litigants in person in the system who, without legal advice, feel cornered when served with a petition blaming them for the marriage breakdown and conclude (wrongly) that they must defend a petition because they think that they will get a worse outcome with the children or money aspects if they don’t defend. It is time to end the blame game.”

Sir James Munby, president of the family division of the high court, told a Westminster legal policy forum conference on Wednesday that he also backed no-fault divorce and called for legislation to introduce it.